Convolutional Neural Networks to Study Contrast-Enhanced Magnetic Resonance Imaging-Based Skeletal Calf Muscle Perfusion in Peripheral Artery Disease

Peripheral artery disease (PAD) is associated with impaired blood flow in the lower extremities and histopathologic changes of the skeletal calf muscles, resulting in abnormal microvascular perfusion. We studied the use of convolution neural networks (CNNs) to differentiate patients with PAD from matched controls using perfusion pattern features from contrast-enhanced magnetic resonance imaging (CE-MRI) of the skeletal calf muscles. We acquired CE-MRI based skeletal calf muscle perfusion in 56 patients (36 patients with PAD and 20 matched controls). Microvascular perfusion imaging was performed after reactive hyperemia at the midcalf level, with a temporal resolution of 409 ms. We analyzed perfusion scans up to 2 minutes indexed from the local precontrast arrival time frame. Skeletal calf muscles, including the anterior muscle, lateral muscle, deep posterior muscle group, and the soleus and gastrocnemius muscles, were segmented semiautomatically. Segmented muscles were represented as 3-dimensional Digital Imaging and Communications in Medicine stacks of CE-MRI perfusion scans for deep learning (DL) analysis. We tested several CNN models for the 3-dimensional CE-MRI perfusion stacks to classify patients with PAD from matched controls. A total of 2 of the best performing CNNs (resNet and divNet) were selected to develop the final classification model. A peak accuracy of 75% was obtained for resNet and divNet. Specificity was 80% and 94% for resNet and divNet, respectively. In conclusion, DL using CNNs and CE-MRI skeletal calf muscle perfusion can discriminate patients with PAD from matched controls. DL methods may be of interest for the study of PAD.

A machine learning-based approach to identify peripheral artery disease using texture features from contrast-enhanced magnetic resonance imaging

Diagnosing and assessing the risk of peripheral artery disease (PAD) has long been a focal point for medical practitioners. The impaired blood circulation in PAD patients results in altered microvascular perfusion patterns in the calf muscles which is the primary location of intermittent claudication pain. Consequently, we hypothesized that changes in perfusion and increase in connective tissue could lead to alterations in the appearance or texture patterns of the skeletal calf muscles, as visualized with non-invasive imaging techniques. We designed an automatic pipeline for textural feature extraction from contrast-enhanced magnetic resonance imaging (CE-MRI) scans and used the texture features to train machine learning models to detect the heterogeneity in the muscle pattern among PAD patients and matched controls. CE-MRIs from 36 PAD patients and 20 matched controls were used for preparing training and testing data at a 7:3 ratio with cross-validation (CV) techniques. We employed feature arrangement and selection methods to optimize the number of features. The proposed method achieved a peak accuracy of 94.11% and a mean testing accuracy of 84.85% in a 2-class classification approach (controls vs. PAD). A three-class classification approach was performed to identify a high-risk PAD sub-group which yielded an average test accuracy of 83.23% (matched controls vs. PAD without diabetes vs. PAD with diabetes). Similarly, we obtained 78.60% average accuracy among matched controls, PAD treadmill exercise completers, and PAD exercise treadmill non-completers. Machine learning and imaging-based texture features may be of interest in the study of lower extremity ischemia.

Longitudinal Magnetic Resonance Imaging-Based Superficial Femoral Artery Velocity Measurements in Diabetic and Nondiabetic Patients With Peripheral Artery Disease

BACKGROUND

Longitudinal associations of noninvasive 2-dimensional phase-contrast magnetic resonance imaging (2D-PC-MRI) velocity markers of the superficial femoral artery (SFA) were analyzed along with the characteristics of peripheral artery disease (PAD). We hypothesized that the 2-year differences in MRI-based measures of SFA velocity were associated with longitudinal changes in markers of PAD.

METHODS

A total of 33 (11 diabetic, 22 nondiabetic) patients with PAD with baseline and 2-year follow-up MRI scans were included in this secondary analysis of the Effect of Lipid Modification on Peripheral Artery Disease after Endovascular Intervention Trial (ELIMIT). Electrocardiographically gated 2D-PC-MRI was performed at a proximal and a distal location of the distal SFA territory. SFA lumen, wall, and total vessel volumes and the normalized wall index (NWI) were analyzed.

RESULTS

Baseline characteristics did not differ between diabetic and nondiabetic PAD patients. Maximum proximal and distal SFA velocity measures did not differ between baseline and 2 years (41.98 interquartile range (IQR) (23.58-72.6) cm/s vs. 40.31 IQR (26.69-61.29) cm/s; P = 0.30). Pooled analysis (N = 33) showed that the 24-month change in the NWI was inversely associated with the 24-month change in the proximal maximal SFA velocity (beta = -168.36, R2 = 0.150, P value = 0.03). The 24-month change of the maximum velocity differences between the proximal and distal SFA locations was inversely associated with the 24-month changes in peak walking distance (beta = -0.003, R2 = 0.360, P value = 0.011).

CONCLUSION

The 2-year change of SFA plaque burden is inversely associated with the 2-year change of proximal peak SFA blood flow velocity. 2D-PC-MRI measured SFA velocity may be of interest in assessing PAD longitudinally.

Extraction of oil, carotenes and tocochromanols from oil palm (Elaeis guineensis) fruit with subcritical propane

This work aims to screen the extraction of oil and bioactive compounds including carotenes and tocochromanols from oil palm fruit with subcritical propane and without using a cosolvent. The overall extraction curves of palm oil with subcritical propane were studied and compared to those extracted with supercritical carbon dioxide. Carotenes and tocochromanols were evaluated not only in the extracted oil, but also in the oil of residual fiber in order to calculate the efficiency to recover these valuable compounds. The experimental results showed that oil yield of up to 70 % could be obtained within 120 minutes with subcritical propane at 50 bar and a flow rate of 35 kg·h−1·kg−1. It was also shown that compressed propane is an excellent solvent for the extraction of oil enriched in carotenes and tocochromanols. Subcritical propane extraction can be used as an alternative process for the simultaneous recovery of these valuable minor components from palm fruit.

Magnetic Resonance Imaging-Derived Microvascular Perfusion Modeling to Assess Peripheral Artery Disease

Background Computational fluid dynamics has shown good agreement with contrast-enhanced magnetic resonance imaging measurements in cardiovascular disease applications. We have developed a biomechanical model of microvascular perfusion using contrast-enhanced magnetic resonance imaging signal intensities derived from skeletal calf muscles to study peripheral artery disease (PAD). Methods and Results The computational microvascular model was used to study skeletal calf muscle perfusion in 56 individuals (36 patients with PAD, 20 matched controls). The recruited participants underwent contrast-enhanced magnetic resonance imaging and ankle-brachial index testing at rest and after 6-minute treadmill walking. We have determined associations of microvascular model parameters including the transfer rate constant, a measure of vascular leakiness; the interstitial permeability to fluid flow which reflects the permeability of the microvasculature; porosity, a measure of the fraction of the extracellular space; the outflow filtration coefficient; and the microvascular pressure with known markers of patients with PAD. Transfer rate constant, interstitial permeability to fluid flow, and microvascular pressure were higher, whereas porosity and outflow filtration coefficient were lower in patients with PAD than those in matched controls (all P values ≤0.014). In pooled analyses of all participants, the model parameters (transfer rate constant, interstitial permeability to fluid flow, porosity, outflow filtration coefficient, microvascular pressure) were significantly associated with the resting and exercise ankle-brachial indexes, claudication onset time, and peak walking time (all P values ≤0.013). Among patients with PAD, interstitial permeability to fluid flow, and microvascular pressure were higher, while porosity and outflow filtration coefficient were lower in treadmill noncompleters compared with treadmill completers (all P values ≤0.001). Conclusions Computational microvascular model parameters differed significantly between patients with PAD and matched controls. Thus, computational microvascular modeling could be of interest in studying lower extremity ischemia.

Comparison of Longitudinal Skeletal Thigh Muscle Findings With Magnetic Resonance Imaging in Patients With Peripheral Artery Disease With-Versus-Without Diabetes Mellitus

The aim of this secondary analysis of ELIMIT (The Effect of Lipid Modification on Peripheral Artery Disease after Endovascular Intervention Trial) was to determine longitudinal changes over 24 months in skeletal thigh muscle volumes and individual muscle compartments in patients with peripheral artery disease (PAD) with and without diabetes. A total of 48 patients with available magnetic resonance imaging of the distal superficial femoral artery at baseline and 2 years were included in this analysis. Muscle volumes and superficial femoral artery wall, lumen, and total vessel volumes were quantified. Intrareader reproducibility of muscle tracings was assessed with the intraclass correlation coefficient using a 2-way model. Baseline characteristics were similar between patients with PAD with and without diabetes, except for smoking history (p = 0.049), cholesterol levels (p <0.050), and calf walking pain (p = 0.049). Interobserver reproducibility of the muscle volume tracings was excellent for all muscle groups (all intraclass correlation coefficients >0.86, confidence interval 0.69 to 0.94). Total muscle and total leg volumes increased significantly between baseline and 24 months among patients with PAD without diabetes (31 ± 6.4 cm³ vs 32 ± 7.0 cm³, p <0.001; 18 ± 4.4 cm³ vs 19 ± 4.8 cm³, p = 0.045), whereas there was no change in patients with PAD and diabetes. Total muscle volume was inversely associated with age and body mass index in patients with PAD both with and without diabetes (p <0.05). In conclusion, magnetic resonance imaging-quantified thigh muscle volumes are highly reproducible and may be of interest in assessing PAD patients with and without diabetes.

Imaging Approaches to the Diagnosis of Vascular Diseases

PURPOSE OF REVIEW

Vascular imaging is a complex field including numerous modalities and imaging markers. This review is focused on important and recent findings in atherosclerotic carotid artery plaque imaging with an emphasis on developments in magnetic resonance imaging (MRI) and computed tomography (CT).

RECENT FINDINGS

Recent evidence shows that carotid plaque characteristics and not only established measures of carotid plaque burden and stenosis are associated independently with cardiovascular outcomes. On carotid MRI, the presence of a lipid-rich necrotic core (LRNC) has been associated with incident cardiovascular disease (CVD) events independent of wall thickness, a traditional measure of plaque burden. On carotid MRI, intraplaque hemorrhage (IPH) presence has been identified as an independent predictor of stroke. The presence of a fissured carotid fibrous cap has been associated with contrast enhancement on CT angiography imaging. Carotid artery plaque characteristics have been associated with incident CVD events, and advanced plaque imaging techniques may gain additional prominence in the clinical treatment decision process.

Relation of Magnetic Resonance Imaging Based Arterial Signal Enhancement to Markers of Peripheral Artery Disease

Peripheral artery disease (PAD) is associated with impaired lower extremity function. We hypothesized that contrast-enhanced magnetic resonance imaging (CE-MRI) based arterial signal enhancement (SE) measures are associated with markers of PAD. A total of 66 participants were enrolled, 10 were excluded due to incomplete data, resulting in 56 participants for the final analyses (36 PAD, 20 matched controls). MR imaging was performed postreactive hyperemia using bilateral thigh blood-pressure cuffs. First pass-perfusion images were acquired at the mid-calf region with a high-resolution saturation recovery gradient echo pulse sequence, and arterial SE was measured for the lower extremity arteries. As expected, peak walking time (PWT) was reduced in PAD patients compared with controls (282 [248 to 317] sec, vs 353 [346 to 360] sec; p = 0.002), and postexercise ankle brachial index (ABI) decreased in PAD patients but not in controls (PAD: 0.75 ± 0.2, 0.60 [0.5 to 0.7]; p <0.001; vs Controls: 1.17 ± 0.1, 1.19 [1.1 to 1.2]; p = 0.50). Intraclass correlation coefficients were excellent for inter- and intraobserver variability of arterial tracings (n = 10: 0.95 (95%-confidence interval [CI]: 0.94 to 0.96), n = 9: 1.0 (CI: 1.0 to 1.0). Minimum arterial SE was reduced in PAD patients compared with matched controls (128 [110 to 147] A.U. vs 192 [149 to 234] A.U., p = 0.003). Among PAD patients but not in controls the maximum arterial SE was associated with the estimated glomerular filtration rate (eGFR), a marker of renal function (n = 36, ß = 1.37, R² = 0.12, p = 0.025). In conclusion, CE-MRI first-pass arterial perfusion is impaired in PAD patients compared with matched controls and associated with markers of lower extremity ischemia.

Associations Between Carotid Artery Plaque Burden, Plaque Characteristics, and Cardiovascular Events: The ARIC Carotid Magnetic Resonance Imaging Study

Importance

It remains unknown whether in an asymptomatic community-based cohort magnetic resonance imaging (MRI) measures of plaque characteristics are independently associated with incident cardiovascular disease (CVD) events when adjusted for carotid artery (CA) wall thickness, a measure of plaque burden.

Objective

To assess associations of CA MRI plaque characteristics with incident CVD events.

Design, Setting, and Participants

The Atherosclerosis Risk in Communities (ARIC) study is a prospective epidemiologic study of the incidence of CVD in 15 792 adults of which 2066 women and men were enrolled in the ARIC Carotid MRI substudy. ARIC participants were enrolled from 1987 to 1989, and the substudy was conducted between January 2004 and December 2005. Analysis began January 2017 and ended August 2020.

Exposures

Incident CVD events during a median (interquartile range [IQR]) follow-up time of 10.5 (8.1-10.9) years were assessed.

Main Outcomes and Measures

Proportional hazards Cox analyses were performed to ascertain associations between MRI variables of CA plaque burden and plaque characteristics.

Results

Of 15 792 ARIC participants, 2066 were enrolled in the substudy, of whom 1256 (701 women [55.8%]) had complete data and were eligible for incident CVD analyses. Carotid artery plaques in participants with incident CVD events (172 [13.7%]) compared with those without (1084 [86.3%]) had a higher normalized wall index (median [IQR], 0.48 [0.36-0.62] vs 0.43 [0.34-0.55]; P = .001), maximum CA wall thickness (median [IQR], 2.22 [1.37-3.52] mm vs 1.96 [1.29-2.85] mm; P = .01), maximum CA stenosis (median [IQR], 5% [0%-22%] vs 0% [0%-13%]; P < .001), and when present, a larger lipid core volume (median [IQR], 0.05 [0.02-0.11] mL vs 0.03 [0.01-0.07] mL; P = .03), respectively. The presence of a lipid core was independently associated with incident CVD events when adjusted for traditional CVD risk factors and maximum CA wall thickness (hazard ratio, 2.48 [95% CI, 1.36-4.51]; P = .003), whereas the presence of calcification was not. The frequency of intraplaque hemorrhage presence in this population of individuals free of CVD at baseline who were not recruited for carotid stenosis was too small to draw any meaningful conclusions (intraplaque hemorrhage presence: 68 of 1256 participants [5.4%]). Carotid artery lumen area and maximum stenosis, which were overall low, were independently associated with incident CVD events when adjusted for traditional CVD risk factors, as anticipated.

Conclusions and Relevance

The presence of a CA lipid core on MRI is associated with incident CVD events independent of maximum CA wall thickness in asymptomatic participants.

Myocardial Extracellular Volume Fraction Adds Prognostic Information Beyond Myocardial Replacement Fibrosis

BACKGROUND

Cardiac magnetic resonance techniques permit quantification of the myocardial extracellular volume fraction (ECV), representing a surrogate marker of reactive interstitial fibrosis, and late gadolinium enhancement (LGE), representing replacement fibrosis or scar. ECV and LGE have been independently linked with heart failure (HF) events. In deriving ECV, coronary artery disease type LGE, but not non-coronary artery disease type LGE, has been consistently excluded. We examined the associations between LGE, global ECV derived from myocardial tissue segments free of any detectable scar, and subsequent HF events.

METHODS

Mid short-axis T1 maps were divided into 6 cardiac segments, each classified as LGE absent or present. Global ECV was derived from only segments without LGE. ECV was considered elevated if >30%, the upper 95% bounds of a reference group without known cardiac disease (n=28). Patients were divided into 4 groups by presence of elevated ECV and of any LGE. Subsequent HF hospitalization and any death were ascertained. Their relationship with ECV was examined separately and as a composite with Cox proportional hazard models.

RESULTS

Of 1604 serial patients with T1 maps, 1255 were eligible after exclusions and followed over a median 26.3 (interquartile range, 15.9-37.5) months. Patients with elevated ECV had increased risk for death (hazard ratio [HR] 2.45 [95% CI, 1.76-3.41]), HF hospitalization (HR, 2.45 [95% CI, 1.77-3.40]), and a combined end point of both outcomes (HR, 2.46 [95% CI, 1.94-3.14]). After adjustments for covariates including LGE, the relationship persisted for death (HR, 1.82 [95% CI, 1.28-2.59]), hospitalization (HR, 1.60 [95% CI, 1.12-2.27]), and combined end points (HR, 1.73 [95% CI, 1.34-2.24]).

CONCLUSIONS

ECV measures of diffuse myocardial fibrosis were associated with HF outcomes, despite exclusion of replacement fibrosis segments from their derivation and even among patients without any scar. ECV may have a synergistic role with LGE in HF risk assessment.

Magnetic resonance imaging based modeling of microvascular perfusion in patients with peripheral artery disease

Peripheral artery disease (PAD) is associated with an increased risk of adverse cardiovascular events, impaired lower extremity blood flow and microvascular perfusion abnormalities in the calf muscles which can be determined with contrast-enhanced magnetic resonance imaging (CE-MRI). We developed a computational model of the microvascular perfusion in the calf muscles. We included 20 patients (10 PAD, 10 controls) and utilized the geometry, mean signal intensity and arterial input functions from CE-MRI calf muscle perfusion scans. The model included the microvascular pressure (pv), outflow filtration coefficient (OFC), transfer rate constant (kt), porosity (φ), and the interstitial permeability (Ktissue). Parameters were fitted and the simulations were compared across PAD patients and controls. Intra-observer reproducibility of the simulated mean signal intensities was excellent (intraclass correlation coefficients >0.995). kt and Ktissue were higher in PAD patients compared with controls (4.72 interquartile range (IQR) 3.33, 5.56 vs. 2.47 IQR 2.10, 2.85; p = 0.003; and 3.68 IQR 3.18, 4.41 vs. 1.81 IQR 1.81, 1.81; p < 0.001). Conversely, porosity (φ) was lower in PAD patients compared with controls (0.52 IQR 0.49, 0.54 vs. 0.61 IQR 0.58, 0.64; p = 0.016). Porosity (φ) was correlated with the ankle brachial index (r = 0.64, p = 0.011). The proposed computational microvascular model is robust and reproducible, and essential model parameters differ significantly between PAD patients and controls.

Enzymatic Detoxification using Lipophilic Hollow-Fiber Membranes: IV. Glutathione Conjugation Reactions

A hollow-fiber technique was used in the enzymatic glutathione conjugation of lipophilic toxins. Native enzyme was circulated on the external side of a lipophilic hollow-fiber membrane while the toxin-containing media (blood, plasma or aqueous solution) were circulated inside the fiber. Glutathione conjugation reactions were catalyzed by rat liver cytosol, with a specific glutathione transferase activity of 40 nmol/min/mg protein (acceptor: 1,2-epoxy-3-(p-nitrophenoxy)propane). Clearance rates of 1,2-epoxy-3-(p-nitrophenoxy)propane, phenylglycidether, styrene oxide, cis-9, 10-epoxystearic acid, cis-9, 10-epoxystearic acid methyl ester, 5a, 6a-cholesterol oxide, 16-, 17a-pregnenolone oxide, and p-nitrobenzylchloride were 10.44, 13.37, 32.25, 7.60, 7.31, 3.92, 4.20 and 29.24 nmol/mg protein/h/cm2 hollow-fiber surface respectively. This technique makes possible glutathione conjugation reactions with crude enzyme preparations over long periods without loss of activity from covalent immobilization and without loss of cofactor from (auto)oxidation. The lipophilic membrane ensures the absence of hemolysis, immunological hazards and hormone loss, while elimination of the toxin is not impaired.

Patient-Specific Flow Descriptors and Normalized wall index in Peripheral Artery Disease: a Preliminary Study

Background and Aims

MRI-based hemodynamics have been applied to study the relationship between time-averaged wall shear stresses (TAWSS), oscillatory shear index (OSI) and atherosclerotic lesions in the coronary arteries, carotid artery, and human aorta. However, the role of TAWSS and OSI are poorly understood in lower extremity arteries. The aim of this work was to investigate the feasibility of hemodynamic assessment of the superficial femoral artery (SFA) in patients with peripheral artery disease (PAD) and we hypothesized that there is an association between TAWSS and OSI, respectively, and atherosclerotic burden expressed as the normalized wall index (NWI).

Methods

Six cases of 3D vascular geometries of the SFA and related inlet/outlet flow conditions were extracted from patient-specific MRI data including baseline, 12 and 24 months. Blood flow simulations were performed to compute flow descriptors, including TAWSS and OSI, and NWI.

Results

NWI was correlated positively with TAWSS (correlation coefficient: r = 0.592; p < 0.05). NWI was correlated negatively with OSI (correlation coefficient: r = -0.310, p < 0.01). Spatially averaged TAWSS and average NWI increased significantly between baseline and 24-months, whereas OSI decreased over 2-years.

Conclusions

In this pilot study with a limited sample size, TAWSS was positively associated with NWI, a measure of plaque burden, whereas OSI showed an inverse relationship. However, our findings need to be verified in a larger prospective study. MRI-based study of hemodynamics is feasible in the superficial femoral artery.

Magnetic resonance imaging-based computational modelling of blood flow and nanomedicine deposition in patients with peripheral arterial disease

Peripheral arterial disease (PAD) is generally attributed to the progressive vascular accumulation of lipoproteins and circulating monocytes in the vessel walls leading to the formation of atherosclerotic plaques. This is known to be regulated by the local vascular geometry, haemodynamics and biophysical conditions. Here, an isogeometric analysis framework is proposed to analyse the blood flow and vascular deposition of circulating nanoparticles (NPs) into the superficial femoral artery (SFA) of a PAD patient. The local geometry of the blood vessel and the haemodynamic conditions are derived from magnetic resonance imaging (MRI), performed at baseline and at 24 months post intervention. A dramatic improvement in blood flow dynamics is observed post intervention. A 500% increase in peak flow rate is measured in vivo as a consequence of luminal enlargement. Furthermore, blood flow simulations reveal a 32% drop in the mean oscillatory shear index, indicating reduced disturbed flow post intervention. The same patient information (vascular geometry and blood flow) is used to predict in silico in a simulation of the vascular deposition of systemically injected nanomedicines. NPs, targeted to inflammatory vascular molecules including VCAM-1, E-selectin and ICAM-1, are predicted to preferentially accumulate near the stenosis in the baseline configuration, with VCAM-1 providing the highest accumulation (approx. 1.33 and 1.50 times higher concentration than that of ICAM-1 and E-selectin, respectively). Such selective deposition of NPs within the stenosis could be effectively used for the detection and treatment of plaques forming in the SFA. The presented MRI-based computational protocol can be used to analyse data from clinical trials to explore possible correlations between haemodynamics and disease progression in PAD patients, and potentially predict disease occurrence as well as the outcome of an intervention.

Morphometric analysis of calcification and fibrous layer thickness in carotid endarterectomy tissues

BACKGROUND

Advanced atherosclerotic lesions are commonly characterized by the presence of calcification. Several studies indicate that extensive calcification is associated with plaque stability, yet recent studies suggest that calcification morphology and location may adversely affect the mechanical stability of atherosclerotic plaques. The underlying cause of atherosclerotic calcification and the importance of intra-plaque calcium distribution remains poorly understood.

METHOD

The goal of this study was the characterization of calcification morphology based on histological features in 20 human carotid endarterectomy (CEA) specimens. Representative frozen sections (10μm thick) were cut from the common, bulb, internal and external segments of CEA tissues and stained with von Kossa׳s reagent for calcium phosphate. The morphology of calcification (calcified patches) and fibrous layer thickness were quantified in 135 histological sections.

RESULTS

Intra-plaque calcification was distributed heterogeneously (calcification %-area: bulb segment: 14.2±2.1%; internal segment: 12.9±2.8%; common segment: 4.6±1.1%; p=0.001). Calcified patches were found in 20 CEAs (patch size: <0.1mm(2) to >1.0mm(2)). Calcified patches were most abundant in the bulb and least in the common segment (bulb n=7.30±1.08; internal n=4.81±1.17; common n=2.56±0.56; p=0.0007). Calcified patch circularity decreased with increasing size (<0.1mm(2): 0.77±0.01, 0.1-1mm(2): 0.62±0.01, >1.0mm(2): 0.51±0.02; p=0.0001). A reduced fibrous layer thickness was associated with increased calcium patch size (p<0.0001).

CONCLUSIONS

In advanced carotid atherosclerosis, calcification appears to be a heterogeneous and dynamic atherosclerotic plaque component, as indicated by the simultaneous presence of few large stabilizing calcified patches and numerous small calcific patches. Future studies are needed to elucidate the associations of intra-plaque calcification size and distribution with atherothrombotic events.

Postprandial effects on arterial stiffness parameters in healthy young adults

Postprandial lipemia has been associated with acute endothelial dysfunction. Endothelial dysfunction, in turn, is associated with increased arterial stiffness. However, the relationship between postprandial lipemia and acute changes in arterial stiffness has not been extensively investigated. Therefore, we conducted a pilot study on the effects of postprandial lipemia on arterial stiffness in 19 healthy young adults before and after consumption of a high-fat mixed meal. Arterial stiffness was assessed locally with echo-tracking carotid arterial strain (CAS) and globally with carotid–femoral pulse wave velocity (PWV). As assessed by these two benchmark parameters, arterial stiffness did not differ significantly postprandially. However, the arterial distension period (ADP) was significantly lower 2 hours after mixed meal ingestion. In addition, slopes of carotid artery area (CAA) curves were significantly steeper postprandially. Therefore, we concluded that ADP may be a more sensitive marker of arterial stiffness in healthy young adults when compared to PWV and CAS.

The Effect of Lipid Modification on Peripheral Artery Disease after Endovascular Intervention Trial (ELIMIT)

METHODS

A total of 102 patients were randomized to either mono-therapy with simvastatin (40 mg daily) or triple-therapy with simvastatin (40 mg daily), extended-release niacin (1500 mg daily), and ezetimibe (10 mg daily). MRI was performed at baseline and 6, 12, and 24 months. SFA wall, lumen, and total vessel volumes were quantified. MRI-derived SFA parameters and lipids were analyzed with multilevel models and nonparametric tests, respectively.

RESULTS

Baseline characteristics did not differ between mono and triple-therapy groups, except for ethnicity (p = 0.02). SFA wall, lumen, and total vessel volumes increased non-significantly for both groups between baseline and 24-months. Non-high-density lipoprotein cholesterol was significantly reduced at 12 months with triple-therapy compared with mono-therapy (p = 0.01).

CONCLUSION

No significant differences were observed between mono-therapy using simvastatin and triple-therapy with simvastatin, extended-release niacin, and ezetimibe for 24-month changes in SFA wall, lumen, and total vessel volumes.

CLINICAL TRIAL REGISTRATION INFORMATION

NCT00687076; Link: http://clinicaltrials.gov/ct2/show/NCT00687076.

High-fat feeding-induced hyperinsulinemia increases cardiac glucose uptake and mitochondrial function despite peripheral insulin resistance

In obesity, reduced cardiac glucose uptake and mitochondrial abnormalities are putative causes of cardiac dysfunction. However, high-fat diet (HFD) does not consistently induce cardiac insulin resistance and mitochondrial damage, and recent studies suggest HFD may be cardioprotective. To determine cardiac responses to HFD, we investigated cardiac function, glucose uptake, and mitochondrial respiration in young (3-month-old) and middle-aged (MA) (12-month-old) male Ldlr(-/-) mice fed chow or 3 months HFD to induce obesity, systemic insulin resistance, and hyperinsulinemia. In MA Ldlr(-/-) mice, HFD induced accelerated atherosclerosis and nonalcoholic steatohepatitis, common complications of human obesity. Surprisingly, HFD-fed mice demonstrated increased cardiac glucose uptake, which was most prominent in MA mice, in the absence of cardiac contractile dysfunction or hypertrophy. Moreover, hearts of HFD-fed mice had enhanced mitochondrial oxidation of palmitoyl carnitine, glutamate, and succinate and greater basal insulin signaling compared with those of chow-fed mice, suggesting cardiac insulin sensitivity was maintained, despite systemic insulin resistance. Streptozotocin-induced ablation of insulin production markedly reduced cardiac glucose uptake and mitochondrial dysfunction in HFD-fed, but not in chow-fed, mice. Insulin injection reversed these effects, suggesting that insulin may protect cardiac mitochondria during HFD. These results have implications for cardiac metabolism and preservation of mitochondrial function in obesity.

Application of speckle-tracking in the evaluation of carotid artery function in subjects with hypertension and diabetes

BACKGROUND

Speckle-tracking enables direct tracking of carotid arterial wall motion. Timing intervals determined with carotid speckle-tracking and slopes calculated from carotid artery area versus cardiac cycle curves may provide further information on arterial function and stiffness. The proposed arterial stiffness parameters were examined in healthy controls (n = 20), nondiabetic patients with hypertension (n = 20), and patients with type 2 diabetes (n = 21).

METHODS

Bilateral electrocardiographically gated ultrasonograms of the distal common carotid artery were acquired using a 12-MHz vascular probe. Four timing intervals were derived from speckle-tracked carotid arterial strain curves: (1) carotid predistension period, (2) peak carotid arterial strain time, (3) arterial distension period, and (4) arterial diastolic time. In addition, carotid artery area curves were recorded over the cardiac cycle and subdivided into four segments, S1 to S4, relating to arterial distention and contraction periods.

RESULTS

Mean far wall predistension period and peak carotid arterial strain time were more delayed in patients with diabetes and hypertension than in controls. Global mean arterial distension period was prolonged and arterial diastolic time was shorter in patients with hypertension and diabetes than in controls. Slopes of segments S2 and S4 were markedly steeper in the combined group of patients with hypertension and diabetes compared with healthy controls (P = .03 and P = .02, respectively).

CONCLUSIONS

Speckle-tracking-based measures of arterial stiffness may provide potential additive value in assessing vascular function in patients at risk for cardiovascular disease.

Abstract 18: The Effect of Lipid Modification on Peripheral Arterial Disease after Endovascular Intervention Trial (ELIMIT)

BACKGROUND

The Effect of Lipid Modification on Peripheral Arterial Disease after Endovascular Intervention Trial (ELIMIT), a prospective double-blind randomized study, was designed to determine over 24-months, the effects of triple drug lipid modification therapy versus mono therapy on the progression of atherosclerotic lesions in the distal superficial femoral artery (SFA), as assessed by 3.0T magnetic resonance imaging (MRI).

METHODS

A total of 95 patients were randomized to either mono therapy with simvastatin (40mg) or triple therapy with simvastatin (40mg), extended-release niacin (1.5g), and ezetimibe (10mg). MR imaging was performed at baseline, 6-, 12-, and 24-months. SFA wall, lumen, and total vessel volumes were quantified using inter-visit co-registered proton-density-weighted turbo spin echo MRI sequences. MRI derived SFA parameters and lipids were analyzed with multi-level models and non-parametric tests, respectively.

RESULTS

Baseline characteristics did not differ between mono and triple therapy groups, except for ethnicity (Table). There was no difference in adverse cardiovascular events between groups (p=0.99). SFA wall, lumen, and vessel volumes increased non-significantly for both groups between baseline and 24-months. Non-high-density lipoprotein cholesterol showed a larger reduction in triple therapy compared with mono therapy at 12-months (p=0.01).

CONCLUSION

Despite improved atherogenic lipid profiles, there was no significant difference between mono therapy with simvastatin and triple therapy with simvastatin, extended-release niacin, and ezetimibe for the 24-month changes in total SFA wall, lumen, and vessel volumes.

Abstract 510: Morphometrics of Calcification in Carotid Endarterectomy Tissue

Arterial calcification plays a significant role in the pathogenesis of carotid atherosclerotic plaques development. The aim of this study was to provide a detailed analysis of calcification morphology based on histological features in carotid endarterectomy (CEA) specimens. In particular, the emphasis is on calcium nodule size/shape and its relation to tissue and lumen morphologies. These studies will help elucidate the mechanisms of the arterial calcification process.

Representative frozen sections were cut from the common, bifurcation, internal and external segments obtained from 9 CEA samples. Histological stains were used to show the calcified particles, tissue compositions and lipids deposition. The digitized images of sections were warped when necessary to achieve closure of the vessel wall. Image analysis was applied to 2 samples to determine the morphologies of calcium particles (size, shape and perimeter), lumen (area and perimeter) and tissue (area and compositions) using ImageJ. Total non-collagen protein and collagen protein were semi-quantitatively analyzed in one sample.

Calcification occurred predominantly in the bifurcation and internal segments of the CEA, occupying up to 17% of the cross-sectional tissue area. Occassionally, calcification was found in the external branch. The lipids distribution is quite patchy. All calcified particles were contained in the intimal layer of the carotid wall. The lumen area was increased in the bifurcation segment, but it deviated from a patent circular shape. The amount of calcific particles was positively correlated with the tissue area (R2=0.8365, p=0.0015). As the calcium particle increase in size, the shape became more elongated. Collagen accounted for up to 5% of the total non-collagen protein.

Different stages of calcification progression occur at the same time, while the very small sized calcium particle grow in size in all directions, the medium sized particle coalescing with its neighbors to form larger particles. The calcification is accompanied by increase in tissue size and distortion of lumen. Presumably, the kinetics of calcification is determined by the composition of the extracellular matrix and the interstitial cells may play a role in the process.

Adhesive function of newcastle-disease virus hemagglutinin in tumor-host interaction

Infection of metastatic lymphoma cells (ESbL) by a low dose of a non-lytic strain of Newcastle disease virus (NDV) leads to viral replication followed by strong cell surface expression of viral antigens, especially hemagglutinin neuraminidase (HN). The expressed HN was functional and facilitated cell-cell interactions and cell attachment. This was shown for NDV infected tumor cells, lymphocytes, fibroblasts and endothelial cells. The interactions could be strongly inhibited by antibodies against the viral HN protein. Increased binding was also seen with HN c-DNA transfectants expressing the HN as the only viral protein. Viral infection did not influence proliferation and lysability of the infected tumor cells. Following intravenous injection of tumor cells, the number of hepatic metastases was significantly reduced when the cells had been pre-infected with NDV. This reduction of metastases correlated with an increased survival time of the animals. As potential mechanisms of these NDV effects we propose augmentation of cell-eel interactions and immune functions and reduction of invasive capacity of NDV infected, as compared to non-infected tumor cells.

GAB2 induces tumor angiogenesis in NRAS-driven melanoma

GAB2 is a scaffold protein with diverse upstream and downstream effectors. MAPK and PI3K signaling pathways are known effectors of GAB2. It is amplified and overexpressed in a variety of human tumors including melanoma. Here we show a previously undescribed role for GAB2 in NRAS-driven melanoma. Specifically, we found that GAB2 is co-expressed with mutant NRAS in melanoma cell lines and tumor samples and its expression correlated with metastatic potential. Co-expression of GAB2(WT) and NRAS(G12D) in melanocytes and in melanoma cells increased anchorage-independent growth by providing GAB2-expressing cells a survival advantage through upregulation of BCL-2 family of anti-apoptotic factors. Of note, collaboration of GAB2 with mutant NRAS enhanced tumorigenesis in vivo and led to an increased vessel density with strong CD34 and VEGFR2 activity. We found that GAB2 facilitiated an angiogenic switch by upregulating HIF-1α and VEGF levels. This angiogenic response was significantly suppressed with the MEK inhibitor PD325901. These data suggest that GAB2-mediated signaling cascades collaborate with NRAS-driven downstream activation for conferring an aggressive phenotype in melanoma. Second, we show that GAB2/NRAS signaling axis is non-linear and non-redundant in melanocytes and melanoma, and thus are acting independent of each other. Finally, we establish a link between GAB2 and angiogenesis in melanoma for the first time. In conclusion, our findings provide evidence that GAB2 is a novel regulator of tumor angiogenesis in NRAS-driven melanoma through regulation of HIF-1α and VEGF expressions mediated by RAS-RAF-MEK-ERK signaling.

Long-term, open-label trial: safety and efficacy of continuous maintenance treatment with pantoprazole for up to 15 years in severe acid-peptic disease

BACKGROUND

To date, the safety and tolerability of proton pump inhibitors (PPIs) have been demonstrated in studies of up to 10 years.

AIM

To report on the tolerability, safety and efficacy of up to 15 years' continuous treatment with pantoprazole in patients with severe acid-peptic disease.

METHODS

Following healing of endoscopically confirmed peptic ulcer or reflux oesophagitis during 4-12 weeks' treatment with pantoprazole (40-80 mg/day), adult patients received open-label maintenance treatment with pantoprazole (40-160 mg/day) for up to 15 years in a single centre combined study (10-year initial study; 5-year extension study). Safety assessments were carried out using endoscopy, clinical examination, clinical laboratory investigations, serum gastrin determination, gastric mucosal histology and mucosal endocrine cell quantification.

RESULTS

The safety set comprised 142 patients. At 12 weeks, healing rates were 95.8%. During long-term treatment, mean fasting gastrin levels rose from baseline to moderate levels throughout the study. Mean enterochromaffin-like cell density showed a moderate initial increase during the first 3 years, remaining stable thereafter. These changes were not associated with any clinically relevant changes of the gastric mucosa. Patients with successful Helicobacter pylori eradication showed long-term regression of antral and corpus gastritis during continued pantoprazole treatment.

CONCLUSIONS

Daily pantoprazole maintenance therapy for up to 15 years for severe acid-peptic disease is effective and well tolerated, with no identified safety concerns. The longest study to date, these data provide reassuring evidence for the long-term safety of pantoprazole.

Benefits and costs of improved IEQ in U.S. offices

This study estimates some of the benefits and costs of implementing scenarios that improve indoor environmental quality (IEQ) in the stock of U.S. office buildings. The scenarios include increasing ventilation rates when they are below 10 or 15 l/s per person, adding outdoor air economizers and controls when absent, eliminating winter indoor temperatures >23°C, and reducing dampness and mold problems. The estimated benefits of the scenarios analyzed are substantial in magnitude, including increased work performance, reduced Sick Building Syndrome symptoms, reduced absence, and improved thermal comfort for millions of office workers. The combined potential annual economic benefit of a set of nonoverlapping scenarios is approximately $20 billion. While the quantitative estimates have a high uncertainty, the opportunity for substantial benefits is clear. Some IEQ improvement measures will save energy while improving health or productivity, and implementing these measures should be the highest priority.

PRACTICAL IMPLICATIONS

Owners, designers, and operators of office buildings have an opportunity to improve IEQ, health, work performance, and comfort of building occupants and to obtain economic benefits by improving IEQ. These benefits can be achieved with simultaneous energy savings or with only small increases in energy costs.

Automatic quantification of muscle volumes in magnetic resonance imaging scans of the lower extremities

Muscle volume measurements are essential for an array of diseases ranging from peripheral arterial disease, muscular dystrophies, neurological conditions to sport injuries and aging. In the clinical setting, muscle volume is not routinely measured due to the lack of standardized ways for its repeatable quantification. In this paper, we present magnetic resonance muscle quantification (MRMQ), a method for the automatic quantification of thigh muscle volume in magnetic resonance imaging (MRI) scans. MRMQ integrates a thigh segmentation and nonuniform image gradient correction step, followed by feature extraction and classification. The classification step leverages prior probabilities, introducing prior knowledge to a maximum a posteriori classifier. MRMQ was validated on 344 slices taken from 60 MRI scans. Experiments for the fully automatic detection of muscle volume in MRI scans demonstrated an averaged accuracy, sensitivity and specificity for leave-one-out cross-validation of 88.3%, 93.6% and 87.2%, respectively.

Simultaneous bilateral magnetic resonance imaging of the femoral arteries in peripheral arterial disease patients

PURPOSE

To image the femoral arteries in peripheral arterial disease (PAD) patients using a bilateral receive coil.

MATERIALS AND METHODS

An eight-channel surface coil array for bilateral MRI of the femoral arteries at 3T was constructed and evaluated.

RESULTS

The bilateral array enabled imaging of a 25-cm segment of the superficial femoral arteries (SFA) from the profunda to the popliteal. The array provided improved the signal-to-noise ratio (SNR) at the periphery and similar SNR in the middle of a phantom compared to three other commercially available coils (4-channel torso, quadrature head, whole body). Multicontrast bilateral images of the in vivo SFA with 1 mm in-plane resolution made it possible to directly compare lesions in the index SFA to the corresponding anatomical site in the contralateral vessel without repositioning the patient or coil. A set of bilateral time-of-flight, T1-weighted, T2-weighted, and proton density-weighted images was acquired in a clinically acceptable exam time of ≈45 minutes.

CONCLUSION

The developed bilateral coil is well suited for monitoring dimensional changes in atherosclerotic lesions of the SFA.